FAQs

Oyster Bay’s waterways are valuable assets to the community and provide important habitat for aquatic species.

Council has prepared this Waterways Management Plan to provide for the holistic and sustainable management of the catchment and waterways to ensure that the waterway health is maintained and remains enjoyable for all.

The study area for the Plan encompasses Oyster Bay, Oyster Creek and Kareela Creek, as shown in the study area map.

We have considered several sources of information to gain an understanding of the key issues affecting the Oyster Bay waterways and the potential causes of observed issues, including:

• Historical aerial imagery and navigation charts;
• Historical survey data and flood studies; and
• Community and waterway user feedback.

Additionally, as part of this project, some specialist investigations were completed, including:

• Up to date survey of the Oyster Bay waterways to map the current bed levels and for comparison with historical surveys. This enabled estimation of the amount and rate of sedimentation that has occurred over time;
• An assessment of sedimentary contamination to inform any potential dredging options; and
• Computer-based modelling of catchment water quality and hydrology to estimate annual sediment loads entering the bay.

The input from the community has played a crucial role in helping the study team interpret the data collected.

Based on evaluation of bed level survey data, catchment modelling and information provided by the community, it is apparent that sediments are transported down the creeks and into the bay. While sedimentation and very gradual infilling of estuaries is a naturally occurring process, it is thought that historic land use change and other activities that impacted the catchment have significantly accelerated the transport of sediments into the bay, leading to shallowing of the upper reaches of the bay.

The draft Waterways Management Plan commissioned by Council has investigated these issues and attempted to identify the key sources and causes of sedimentation.

The build-up of sediment in Oyster Bay has adversely impacted boating, kayaking and other recreational activities, with members of the public having been stranded on the mudflats as the water retreats at low tide. The fine, muddy material in these shallow flats is extremely difficult to walk through, making it challenging to access stranded people. In other locations, although the bed is not exposed over the low tide, the shallowing of the Bay has limited navigational access, even for small watercraft.

Dredging is the process of removing sediment build-up from a waterway. It is usually carried out with specialised dredging vessels or excavators. Dredging may be undertaken for purposes of navigational access or environmental reasons.

There are alternative options that may address the accumulation of sediments in the Oyster Bay waterways, which include catchment-based strategies that target the source of sediments.

Catchment-based solutions may include water quality treatment devices, which capture eroded sediments and other pollutants, or water sensitive urban design features which incorporate natural features that better suit sensitive environments.

In developing the Oyster Bay Waterways Management Plan, Council has explored management strategies to enhance waterway health based on scientific data, community input, and user feedback, including measures to reduce sedimentation. 

The Oyster Bay Dredging Management Plan has been included in the Waterways Management Plan to provide more detailed consideration of dredging options, assessing continuous maintenance strategies for the bay and its upstream waterways, and evaluating implementation feasibility in line with Council’s Dredging Policy. 

Both plans are presented together to provide a comprehensive approach to managing Oyster Bay waterways. On our Join the Conversation page, the plans are downloadable in sections so you can explore them more easily.

For Oyster Bay, it will be important that the objectives and actions of the Waterways Management Plan are consistent with the Georges River Coastal Management Program and any Floodplain Management Plans covering the creeks and watercourses draining to Oyster Bay (including Oyster Creek, Kareela Creek and overland flow areas within the catchment).

For actions in the Waterways Management Plan to be funded through the Coastal and Estuary Grants Program or the Floodplain Management Grants Program, then the same actions will need to be specifically identified in the relevant Coastal Management Program or Flood Risk Management Plan.

Council may also pursue other funding sources, or self-fund the actions of the Waterways Management Plan.

We heard that Oyster Bay is a highly valued place, central to daily life, identity, and wellbeing for many long-term residents and visitors. People expressed concern about changes in the area over time and the impact on local character.

Feedback highlighted the importance of healthy waterways, good water and sediment quality, and the role Oyster Bay plays in supporting biodiversity, cultural values, and a wide range of recreational uses. 

In response, the draft plans consider actions such as creek dredging and stormwater maintenance to address local drainage issues and manage sources of sediment, while noting the need for caution where changes may affect flooding. 

This work will also be guided by Council’s detailed flood study, which is currently underway.

The feasibility and cost of any dredging activity depends on a range of factors, including the scale, location, and methods used for sediment removal.

Beyond the cost of the actual extraction rate ($/m³), a large cost for most dredging projects is the mobilisation of all equipment needed to the project site. This can be quite significant if the equipment is highly specialised and needs to come from some distance away.

Costs associated with transportation and disposal of material can also be high, depending on distance travelled and where it is placed (e.g., Lucas Heights landfill centre, which can accept contaminated material).

Floating dredgers and slurry pumps are generally the simplest and cheapest method and can be used to extract material where large areas are to be dredged.

This typically requires good water depth and involves mostly clean sandy material.

Bay-wide dredging has been assessed as a high-cost option with limited value for money. Based on current bed levels, achieving a depth of at least -0.8 mAHD (and up to -1.2 mAHD) would require dredging a footprint of approximately 570,000 m². Even with conservative sedimentation estimates of 3 mm per year, ongoing maintenance dredging would still be required—around 8,000 m³ every five years.

The scale and cost of such an undertaking make it unlikely to attract funding through competitive State Government grant programs, which require a strong business case and demonstrable community benefit. In addition to financial challenges, large-scale dredging proposals must also meet stringent environmental planning requirements and show clear socio-economic advantages to justify potential environmental impacts.

As a result, bay-wide dredging is not considered a viable or sustainable option at this time.

Given the above variables, an accurate assessment of feasibility and costs can only be established once a clear dredging plan and specific outcomes are agreed by all interested parties and authorities.

For dredging small areas composed of fine and/or contaminated material, land-based plant is often employed (e.g., long-reach excavators). After careful removal, material can be placed directly into trucks or hoppers for transport.

Dredging via land-based plant would be limited by reach from the shoreline.

Yes. Excavation equipment can sometimes be placed on floating barges, along with hoppers for storing the material. However, adequate water depths (greater than 2 metres) generally limit where this can be done.

Yes. The use of floating dredges may be constrained by access and navigation limits, such as clearance under bridges, as well as depth limitations. A suitable landside area would also be required for dewatering the slurry (the mixture of sediment and water sucked up by the dredge).

Alternatively, the slurry can be held in a tank and disposed of elsewhere, such as another waterway or offshore, subject to strict environmental conditions.

In addition to the physical dredging works, projects of this nature also require:

• detailed pre- and post-works bathymetric surveys
• a range of specific technical investigations to support design and planning approvals (e.g., ecological survey, sediment sampling and laboratory testing)
• engineering design drawings and technical specifications
• a comprehensive environmental assessment and multiple regulatory approvals
• a tendering process
• supervision of works to ensure design objectives are met and the environment remains protected.

All these elements need to be costed when considering the overall feasibility of dredging.

The Oyster Bay Waterways Management Plan is a document to guide actions by Sutherland Shire Council relating to the health, safety, and sustainability of Oyster Bay. It has not been prepared in response to a specific State Government program or directive. Rather, it has been driven by Council with input and consideration by the local community.

A Coastal Management Program (CMP) is a document prepared by a Council under the provisions of the NSW Coastal Management Act 2016. A CMP is prepared for a specific coastal area and sets out actions required to address the objects and objectives of the Act. The CMP is prepared following a documented framework and contains specific content to meet the needs of the Act.

Following endorsement from relevant agencies and stakeholders, the CMP is certified by the Minister responsible for the Act. Actions in the CMP then become eligible for funding under the NSW Coastal and Estuary Grants Program.

A Flood Risk Management Plan is prepared by a Council to guide the management and future use and development of land in accordance with NSW Government’s Flood Prone Lands Policy.

The NSW Government’s Floodplain Management Manual sets out the process for assessing flood risks and developing a flood risk plan that takes account of all important factors, including community engagement and education. Importantly, if a Council follows the process set out in the Manual, it is taken to have acted in good faith and is provided exemptions in liability relating to flooded land as afforded under the Local Government Act 1994 (s733). The NSW Government supports the development and implementation of flood risk 

Council will assess the recommendations of the Waterways Management Plan in light of submissions received during the public exhibition period. After the conclusion of the exhibition period, the Plan will be finalised with a list of actions for implementation. Actions in the endorsed Waterways Management Plan will be incorporated into Council’s capital works and stormwater management programs.